1. Field of the Invention
This invention relates to a printer having a double-sided print function.
The present application is based on Japanese Patent Applications No. Hei. 10-292387 and 11-236686, which are incorporated herein by reference.
2. Description of the Related Art
A laser-beam printer particularly among printers is often used for printing text documents in an office, etc., and thus is designed to be able to print in different modes of not only simple single-sided print, but also double-sided print, multiple-copy print, etc. Methods for speeding up print are also devised actively. Further, various steps to be taken for an error occurring in printing are also developed.
One of related arts for executing double-sided print at high speed is invention of a double-sided image formation apparatus described in Japanese Patent Publication No. Hei. 1-29111. This related art specifically relates to a copy machine for copying an image read from an original bed rather than a printer for receiving print data from a host and interpreting and printing the print data. To make a double-sided copy of a document consisting of a number of pages, one ingenious sequence fitted to high-speed print is adopted for a print sequence as to images on which pages are printed on the face and back of paper in what order. In the print sequence, print is executed in a specific order different from the page order. To enable images on correct pages to be printed on the face and back of paper even in the print order different from the page order, two image memories each for one page corresponding to the face and back of paper are provided and page image read from the face image memory or that from the back image memory is selected in response to a signal related to the transport state transition of paper.
Another relevant related art is Japanese Patent No. 2522799. It discloses steps to be taken if print paper runs out while double-sided print is being executed. That is, if it becomes impossible to supply a new sheet of paper from a paper feed tray while double-sided print is being executed using the same print sequence as in Japanese Patent Publication No. Hei. 1-29111 described above, immediately the print page order following the print sequence is changed so that the sheet of paper whose face is already printed does not remain in the printer for hours, then the sheet of paper whose face is already printed remaining in the printer is fed taking precedence over any other paper, print on the back of the remaining sheet of paper is completed, and the sheet is discharged.
The two related arts described above are control arts specialized only for the print mode in which double-sided print is executed and moreover the number of print copies is one. Since print mode variations are not so many if a copy machine for reading an image from an original bed and printing the image is involved, the design for providing a dedicated control program for realizing a print sequence specialized only for double-sided print of one copy and further providing control programs specialized for other print modes may be reasonable. The design for providing image memories for two pages for the face and back of paper as in Japanese Patent Publication No. Hei. 1-29111 may be sufficiently adoptable considering circumstances where the copy machine would be constant in image resolution and moreover large-capacity memory and a high-performance CPU are easily installed because the copy machine is a high-price product. The method as in Japanese Patent No. 2522799 wherein if a no-paper error occurs during execution of the print sequence specialized only for double-sided print of one copy, immediately the print sequence is stopped and is switched to another sequence for the no-paper error is also adoptable from the viewpoint of the machine capability if the machine has large-capacity memory capable of storing various print sequence control programs responsive to various situations (if enormous manpower required for development of the various control programs is ignored).
However, for the printer, it is becoming considerably difficult to realize the above-described related arts. One of the reasons is that the printer receives print job data from a host and interprets and prints the data and moreover the possible print modes requested by the host are diversified. That is, the printer cannot previously know what print mode is requested by the host, namely, single-sided or double-sided print and the number of print copies. The printer cannot know the print mode until it receives print job data from a host and interprets the data. Moreover, the printer can know only the received page and cannot know even the total number of subsequent pages unreceived. For example, the case is also possible where double-sided print and one as the number of print copies are applied to the first to fourth pages and double-sided print and two as the number of print copies are applied to the fifth page and later. The printer must be able to cover all print modes that can be assumed and moreover also able to cope flexibly with the print mode difference for each page as in the above-given example. Moreover, an appropriate print sequence must be determined in response to the situation on the spot within the range of the information that can be grasped from the current data already received.
Under such circumstances, first the print mode variations that can be assumed are numerous and thus it is practically impossible to develop print sequence control programs fitted to the print modes. Even if it is possible to develop the control programs, extremely large-capacity memory for storing the control programs is required and it is extremely difficult to provide the lower-price printer than the copy machine with the extremely large-capacity memory. Even if it is possible to provide the printer with the extremely large-capacity memory, it is extremely difficult for a CPU to generate image data at high speed and realize high-speed print while frequently selecting, changing, and executing a large number of types of control programs corresponding to various print modes in response to the interpretation result of reception data with the CPU capability allowed in the printer price range.
Since the print image resolution varies from one print job to another in the printer, the technique of providing image memories for two pages for the face and back of paper as in Japanese Patent Publication No. Hei. 1-29111 cannot be adopted at all.
The technique of switching to the print order in another print sequence if an error occurs during execution of a predetermined print sequence in a printer order as in Japanese Patent No. 2522799 cannot be adopted either for the printer hard to provide all print sequences that can be assumed as described above.